Two Refineries App Note中Two Refineries App Note检测方案(能散型XRF)

A Thermo Fisher Scientific Brand8-321 04/2014 A Tale of Two Refineries Jonathan Margalit， PhD， Thermo Scientific Portable Analytical Instruments Fire assay is an established and proven method for testing the purityof gold jewelry and other objects. Nevertheless， it is a destructive andtime-consuming process requiring the use of hazardous chemicals. X-rayfluorescence has emerged as a non-destructive alternative to the fire assaymethod， with comparable accuracy in just minutes.XRF instrumentationis now available in portable units ideally suited for countertop use in retailenvironments for accurate testing of any precious metal. In a test againsttwo different refineries using fire assay to evaluate two gold ingots fromthe same melt， an XRF analyzer provided results just as accurate as onerefinery， and even more accurate than the second refinery. The test resultsprovided in this article were performed using the Thermo ScientificTMNitonTM DXL Precious Metal Analyzer. What is Fire Assay? The livelihood of businesses that buy and recycle gold，such as jewelry stores and pawn brokers， depends onbeing able to determine the accurate karat (K) weight ofgold jewelry. Failing to detect just a small variation incomposition can be an expensive mistake. Many of thesebusinesses use fire assay testing to evaluate their gold，but this method， while an industry standard analyticalprocess， requires many steps. Fire assay is a methodaimed at separating the gold from all the other metals ina given piece of jewelry. Although the gold is retained atthe end of the process， fire assay is a destructive methodthat requires the removal of a small sample from thejewelry item. The sample is weighed and mixed with a flux (such assoda ash or borax) and lead (or silver) in a crucible. Theflux reduces the melting temperature while the lead actsas a collector material. The sample is then heated andmelted at a temperature range of 1000°C-1200°℃， atwhich point the precious metals are collected by themolten lead and settle at the bottom of the crucible as a“lead button，"leaving behind the base metals and otherimpurities in the slag. Gold content analysis using the Niton DXL XRF analyzer (above)and the traditional fire assay method (below). Upon cooling， the lead button is separated from the slag and is placed into a refractory-madeporous cup (“cupel") and heated in a cupellation furnace. During this step the lead is absorbed intothe cupel’s pores， leaving behind a precious metal bead (“prill"). To determine the gold content， thebead is dissolved in nitric acid， separating the gold from silver， or as an alternative， the bead can bedissolved in a mixture of hydrochloric and nitric acids (“aqua regia”). In the latter case the goldcontent can be determined by using one of several analytical methods (AAS，ICPMS， ICPAES). While fire assay is widely used and considered to be one of the most accurate methods to determinethe gold content in jewelry， it requires multiple preparation and processing steps. The method’sreliability and accuracy can only then be guaranteed if these steps are carried out meticulously byskilled operators. Any slight procedural deviations in the course of the fire assay can accumulate toa significant error， as the following example demonstrates. Refineries Provide Conflicting Results The fire assay process is typically performed in large refineries equipped for this type of analysis.However， not all refineries are created equal as one pawn broker found out when two refineriescame up with two significantly different results regarding the content of his precious metal. Thebroker decided to test out a new refinery by sending his current refinery and the new companyingots of gold scrap from the same melt. The new refiner was sent 850g， while the current refinerwas sent 600g.The bar sent to the current refiner was double-fire assayed with a return of 52.7%gold. The new refiner， however， returned 51.2% gold. For this particular transaction， this representsapproximately a $150 difference for the metals. XRF to the Rescue So how does portable XRF compare to fire assay? Prior to being sent to the refineries， both goldingots were tested on the broker’s Niton DXL machine. The DXL analyzer determined the sampleshad a gold content of 52.5%， nearly the same as the current refinery's results. The accuracy of the Niton DXL and XL2 Precious Metal Analyzers is typically within 1/8 of akarat of the fire assay results. In fact， a recent correlation study comparing a Niton instrument tofire assay showed a correlation factor of 0.999. In addition to being a non-destructive method，portable XRF is a much more comprehensive analysis， yet simple， fast， and does not require anyhazardous chemicals When a sample is measured using XRF， each element present in the sample emits its own uniquefluorescent x-ray energy spectrum. By simultaneously measuring the fluorescent x-rays emitted bythe different elements in the sample， XRF analyzers can rapidly determine those elements present inthe sample and their relative concentrations - in other words， the elemental chemistry of thesample， typically in seconds. Conclusion XRF analyzers provide a fast， accurate，and nondestructive method to test the purity andcomposition of gold and other precious metals， with results comparable to the much morecomplicated，lengthy， and as we see in this case， possibly faulty fire assay method.XRF quicklyprovides the exact karat weight and percentages of all elements within an item - easily identifyingnon-standard， under-karated， and even advanced counterfeit material. What’s more， some XRFinstruments feature technology that can identify gold-plated items. thermoscientific.com/niton C 2014 Thermo Fisher Scientific Inc. All rights reserved. All other trademarks are the property of Thermo Fisher Scientific Inc. and its subsidiaries.Specifications， terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details. Americas Europe， Middle East， Asia PacificBoston， MA USA Africa & South Asia New Territories， Hong Kong+19786707460 Munich， Germany +8522885 4613niton@thermofisher.com +49 893681380 .niton.asia@thermofisher.comniton.eur@thermofisher.com In addition to these offices， Thermo Fisher Scientific maintains a network of representative organizations throughout the world. Fire assay is an established and proven method for testing the purity of gold jewelry and other objects. Nevertheless, it is a destructive and time-consuming process requiring the use of hazardous chemicals. X-ray fluorescence has emerged as a non-destructive alternative to the fire assay method, with comparable accuracy in just minutes. XRF instrumentation is now available in portable units ideally suited for countertop use in retail environments for accurate testing of any precious metal. In a test against two different refineries using fire assay to evaluate two gold ingots from the same melt, an XRF analyzer provided results just as accurate as one refinery, and even more accurate than the second refinery. The test results provided in this article were performed using the Thermo Scientific™ Niton™ DXL Precious Metal Analyzer.